This invention relates to a high pressure fuel injection unit for an engine, and more particularly to an improved arrangement for energizing the electromagnetic assemblies of the injection unit which control fuel injection timing and the lift of the injection valve respectively so as to reduce the risk of burning damage to the electromagnetic assemblies and to improve the durability of the injection unit.
One popular form of fuel injection unit for engines is the so-called "accumulator type." This type of injection nozzle includes an accumulator chamber that is charged with fuel under pressure and which communicates with a nozzle port. An injection valve is supported within the accumulator chamber and controls the discharge through the nozzle port. An actuating device is associated with the injection valve and is moveable within a control chamber that is also pressurized with fuel. A valve is associated with the control chamber and is opened so as to reduce the pressure and cause the pressure in the accumulator chamber to unseat the injection valve and initiate fuel injection. Typically, the valve is operated by a main electromagnetic assembly that is contained within the housing of the fuel injection nozzle.
To control the amount of fuel injected, the inventors have proposed to provide an additional and separate sub-electromagnetic assembly within the accumulator chamber to control the lift movement of the injection valve. This assembly is provided with a coil which, when energized, attracts a lift regulating member downward against a holder member which supports the coil to permit only a relatively small upward lift movement of the injection valve to allow injection of a smaller amount of fuel when injection is initiated. On the other hand, when the coil is not energized, the regulating member moves freely within a bore of the holder member so the injection valve is able to move upward a greater distance to permit injection of a larger amount of fuel.
Although previous injection units of this type have been generally satisfactory, effective operation of such units has typically required that regulating member be held down against the holding member with a magnetic flux which is greater than the magnetic flux generated by the main electromagnet during the entire time of small lift operation. Generation of such a large magnetic flux in the sub-electromagnetic coil has typically required that the coil be supplied with a relatively large current during the entire small lift operation. This may cause burning damage to the coil and may also decrease the durability of the coil.
It is, therefore, a principal object of this invention to provide an improved energizing arrangement for an electromagnetic assembly which controls the lift amount of an injection valve so as to eliminate or greatly decrease the likelihood of causing burning damage to the electromagnetic assembly.
It is another object of this invention to provide an improved energizing arrangement for an electromagnetic assembly which controls fuel injection, wherein this electromagnetic assembly does not require a large current for a long period of time during injection process so as to eliminate or greatly decrease the likelihood of causing burning damage to the electromagnetic assembly.